June 2015

Running shoe reveal: Study links max cushioning, higher load

By P.K. Daniel

Researchers from the Spaulding National Running Center at the Harvard Medical School in Cambridge, MA, have found that running in highly cushioned shoes is not associated with lower impact forces than conventional running shoes.

Instead, the investigators found highly cushioned (HC) shoes result in a significantly higher vertical average load rate (VALR) and vertical instantaneous loading rate (VILR), both of which have been associated with overuse injuries such as tibial stress fractures and plantar fasciitis. The findings were presented in May at the annual meeting of the American College of Sports Medicine (ACSM) in San Diego.

The study was inspired by HC shoe manufacturers’ claims that the thicker midsoles reduce the impact of landing during running, said Matthew Ruder, MS, a laboratory engineer at the Spaulding National Running Center, who presented the findings. These shoes are designed with up to 2.5 times more cushioning by volume than the standard running shoe, accounting for less heel-to-toe drop and a more uniform thickness throughout the shoe. The HC shoes used in the ACSM study had a 4-mm heel drop, versus about a 12-mm heel drop in the traditional shoes.

Fourteen healthy male runners (age 31.6 ± 11.2 years), who run on average a minimum of 10 miles per week, were recruited for the ongoing study. All were rearfoot strikers. They ran at a standard self-selected speed (average 2.68 m/s) on an instrumented treadmill under both shoe conditions.

Ruder said the team found little difference between shoes for vertical ground reaction forces. However, running in HC shoes resulted in significantly higher impact loading (VILR and VALR). The peak lateral forces that occur early in the stance, which appeared to be lower in the HC shoes than the traditional shoes when fewer runners were analyzed, also turned out to be significantly higher for the HC shoes. These increased forces may further increase the pronatory moment during early stance.

While counterintuitive, the results are consistent with other studies, the researchers said. In a 2006 study of nine healthy runners, investigators from the University of Florida in Gaines­ville reported that leg stiffness during hopping was significantly greater in a cushioned shoe than barefoot, whereas leg stiffness did not differ significantly between a less-cushioned shoe and barefoot. Those findings were published in the Journal of Athletic Training.

“People actually land softer when they have less cushioning,” said study coauthor Irene S. Davis, PhD, PT, a professor in the Department of Physical Medicine and Rehabilitation at Harvard Medical School and director of the Spaulding National Running Center. “Cushioning actually lulls you into thinking you can slam your foot into the ground.”

The runners were given three minutes on the treadmill to acclimate to each shoe before data from 15 steps were collected. Because the participants were not habituated to the HC shoes, the researchers have more studies planned to see if more time for familiarization has an effect on loading rates.

“We still have much to do,” said Ruder. “This was just a pilot study with runners who don’t run in these shoes. We need to get people who run in these shoes habitually. This will be especially important to know—how people have adapted to running in them over time.”

The researchers plan to look at the kinematics associated with the different shoe cushioning conditions, and also have started to collect accelerometer data at the ankle to examine tibial shock. The results from the accelerometer data will be presented at the annual meeting of the American Society of Biomechanics in August in Columbus, OH.

“I think there will be some interesting results to come out of that as well,” Ruder said.

The study compared a cushioned shoe (Hoka One One) to another cushioned shoe (Nike Pegasus) and found that the cushioned running shoe did not reduce the vertical loading rate when compared to another cushioned running shoe … go figure!

Lowering the heel height probably has more impact (pun intended) on increase in vertical loading than softer (HC) midsole shoes. Of course this is a guess on my part just like the researchers at Spaulding Running Center are also guessing. How and why would they change both the heel offset from 12 mm to 4 mm and also change the cushioning and expect to understand what is causing the increase in vertical loading does not make sense. Introducing multiple changes in shoe design and expect to understand the outcome is counter intuitive. Additionally treadmills increase instability vs running on dirt or more hard pavement. The treadmill acts as a multiplier of shock absorption as well as foot instability.